System and method for battery pack

ABSTRACT

A battery pack includes an arrangement of battery cells organized in battery groups connected in series, with each group having one or more battery units connected in parallel, and each battery unit comprising one or more series-connected battery cells connected to a battery switch. Charging of the battery pack uses pulse charging. The charging pulses provided to the battery units can be determined based on one or more measured characteristics of battery cells comprising the battery unit so that charging of the battery units can be optimized according to those characteristics. The charging pulses provided to each battery group are timed so that there is an uninterrupted flow of charging current through all the battery groups at all times.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application under 35 U.S.C. § 120 ofU.S. patent application Ser. No. 15/861,610, filed on Jan. 3, 2018,which claims priority under 35 U.S.C. § 119(e) to U.S. ProvisionalPatent Application No. 62/442,932, filed on Jan. 5, 2017. The U.S.patent application Ser. No. 15/861,610 is related to commonly owned U.S.patent application Ser. No. 15/644,498, filed on Jul. 7, 2017, now U.S.Pat. No. 10,135,281. The contents of U.S. patent application Ser. No.15/861,610, U.S. patent application Ser. No. 15/644,498, and U.S.Provisional Patent Application No. 62/442,932 are incorporated herein byreference in their entirety.

BACKGROUND

A battery pack typically comprises some configuration of several batterycells. A battery cell typically includes a casing to hold the componentsthe of the battery cell. The battery cell may include an anode (negativeelectrode) immersed in a suitable electrolyte. The anode may compriseany suitable compound such as porous carbon particles; e.g. graphiteparticles arranged into sheets. The battery cell may further include acathode immersed in an electrolyte. The cathode may comprise anysuitable metal oxide compound such as cobalt-oxide (CoO₂) particles.Many types of battery cells are known, but for discussion purposeslithium-ion types will be used.

A battery discharges, for example, when it is connected across a load.During discharging, ions (e.g., lithium ions) flow through theelectrolyte from the negative electrode to the positive electrode.Electrons flow from the negative electrode to the positive electrodethrough the load. The lithium ions and electrons combine at the positiveelectrode. When no more Li ions flow for the given discharge potentialapplied across the cell, the battery can be deemed to be fullydischarged.

During charging, the lithium ions flow from the positive electrode tothe negative electrode through the electrolyte. Electrons flow throughthe external charger in the direction from the positive electrode to thenegative electrode. The electrons and lithium ions combine at thenegative electrode and deposit there. When no more Li ions flow for thegiven charge potential applied across the cell, the battery can bedeemed fully charged and ready to use.

BRIEF DESCRIPTION OF THE DRAWINGS

With respect to the discussion to follow and in particular to thedrawings, it is stressed that the particulars shown represent examplesfor purposes of illustrative discussion, and are presented in the causeof providing a description of principles and conceptual aspects of thepresent disclosure. In this regard, no attempt is made to showimplementation details beyond what is needed for a fundamentalunderstanding of the present disclosure. The discussion to follow, inconjunction with the drawings, makes apparent to those of skill in theart how embodiments in accordance with the present disclosure may bepracticed. Similar or same reference numbers may be used to identify orotherwise refer to similar or same elements in the various drawings andsupporting descriptions. In the accompanying drawings:

FIGS. 1 and 1A depict high level schematics of a battery pack inaccordance with the present disclosure.

FIG. 2 shows details of a battery group in accordance with the presentdisclosure.

FIG. 3 shows details of a control unit in accordance with the presentdisclosure.

FIGS. 4 and 4A illustrate examples of switch configurations.

FIG. 5 illustrates a pulse timing diagram.

FIG. 6 shows an embodiment of a battery pack in accordance with thepresent disclosure.

FIG. 6A shows an embodiment of a battery pack in accordance with thepresent disclosure.

FIG. 7 illustrates a battery group in accordance with the presentdisclosure.

FIGS. 8 and 8A illustrate a battery group in accordance with the presentdisclosure.

FIG. 9 illustrates details for determining the duty cycle of a chargingpulse in accordance with the present disclosure.

FIG. 10 illustrate details for detecting a change in the current flowthrough a battery in accordance with the present disclosure.

FIG. 11 shows processing in the controller for frequency modulatedcharging in accordance with the present disclosure.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerousexamples and specific details are set forth in order to provide athorough understanding of the present disclosure. It will be evident,however, to one skilled in the art that the present disclosure asexpressed in the claims may include some or all of the features in theseexamples, alone or in combination with other features described below,and may further include modifications and equivalents of the featuresand concepts described herein.

FIG. 1 shows an embodiment of a battery pack 1 in accordance with thepresent disclosure. The battery pack 1 may comprise a plurality ofbattery cells 3-11. Each battery cell 3-11 may be connected to acorresponding switching element 12-20 (battery switch); e.g., an FETswitch. The battery cells 3-11 may be organized into M battery groups,group 1, group 2, group m. Each battery group may have N battery cellsconnected in parallel, for a total of M×N battery cells in the batterypack 1. In some embodiments, for example, N may be 2-100. Battery group1, for example, comprises N battery cells 3, 4, . . . 5. Battery group 2comprises N battery cells 6, 7, . . . 8, and so on. In some embodiments,each battery group may have the same number N of battery cells. In otherembodiments, the number N of battery cells may vary from one batterygroup to another. The number M of battery groups can depend on thedesired output voltage V_(BATT) of the battery pack 1. For example, ifthe desired V_(BATT) is 400 V and the battery cells 3-11 are 3.7 Vbatteries, then there will be M=108 battery groups for a V_(BATT) of399.6 V. The battery cells 3-11 may be lithium-ion battery cells. Otherconfigurations of M and N are possible.

During charging of battery pack 1, a charger voltage from a charger 4gets connected to battery pack 1 at terminals 21 and 22. Thisconfiguration is shown in FIG. 1A.

The battery pack 1 may include a control unit 2. In accordance with thepresent disclosure, the control unit 2 may include circuitry to performmeasurements for each battery cell 3-11 in the battery pack 1. Batterycell measurements may be taken for each battery cell in each batterygroup. Each battery group may have a set of measurement lines M_(x) thatfeed into the control unit 2, to allow for each battery cell in thatbattery group to be individually measured. For example, battery group 1may provide a set M₁ of measurement lines, battery group 2 may provide aset of measurement lines M₂, and so on. Battery cell measurements may bedone at time intervals allowing to digitize precise values and dynamicchanges of measured parameters for each battery cell in real time. Aswill be discussed below, the measurements may be used by the controlunit 2 to control the ON (conducting)/OFF (non-conducting) states of theswitching elements 12-20.

The switching elements 12-20 of the battery pack 1 can be controlled bycontrol unit 2. The control unit 2 may output control signals (switchingsignals) for each battery group via a set of switching lines S_(x). Forexample, a set of switching lines S₁ provided to battery group 1 maycomprise a control line for each switching element 12, 13, . . . 14 inbattery group 1, a set of switching lines S₂ provided to battery group 2may comprise a control line for each switching element 15, 16, . . . 17in battery group 2, and so on. During charging of battery pack 1, eachbattery cell 3-11 of the battery pack 1 gets pulse charged via itscorresponding switching element 12-20. In accordance with the presentdisclosure, the switching elements 12-20 of the battery pack 1 may becontrolled such that the charge current from the charger 4 flowing intothe battery pack 1 through terminals 21 and 22 is substantially constantwhile the battery pack is being charged.

In some embodiments, the ON times for the switching elements 12-20 maybe interleaved (or overlap) to keep overall charge current from thecharger 4 flowing into the battery pack 1 substantially constant (e.g.,at a predetermined level) to avoid current fluctuations in the charge,since current fluctuations in certain chargers (e.g., switching typevoltage regulators) can damage the charger. In some embodiments, theswitching elements 12-20 may be operated so that the total chargecurrent from the charger 4 into the battery pack 1 can vary within apredetermined range between a maximum charge current and a minimumcharge current.

Maintaining a substantially constant charge current through battery pack1 at all times during charging allows for the use of battery chargersdesigned for traditional charging protocols such as CCCV (constantcurrent/constant voltage) and the like, while at the same time allowingthe each battery cell in the battery pack to be charged using advancedpulse charging protocols to optimize charging for that battery cell. Forexample, an advanced pulse charging protocol developed by the inventorsmay operate the switching elements 12-20 with ON times in the range from0.5 μS to 100 mS. Such pulse charging protocols in some cases requireOFF durations for battery cell current in the range from 0.5 μS to 1000mS. See for example, commonly owned U.S. application Ser. No. 15/644,498filed Jul. 7, 2017, the content of which is incorporated herein byreference in its entirety for all purposes.

FIG. 2 illustrates details of a battery group, for example battery group1, in accordance with some embodiments of the present disclosure. Thefigure shows that the set of measurement lines M₁ may comprise pairs ofsense lines to sense voltages across respective corresponding batterycells 3-5 in battery group 1. For example, sense lines M₁₋₄ areconnected across battery cell 14. Although not shown, it will beunderstood that in some embodiments, the measurement lines may includesense lines for each battery cell to measure the current flow throughthat battery cell. More generally, measurement lines can be provided tomeasure any characteristic of the battery cell. FIG. 2 further shows theset of switching lines S₁ may comprise respective switching controllines to control the ON/OFF state of each switching element 12, 13, . .. 14 connected to the corresponding battery cells 3, 4, . . . 5 inbattery group 1.

FIG. 3 illustrates details of the control unit 2 in accordance with someembodiments. The control unit 2 may include a selector 302. Themeasurement lines M_(x) feed in the selector 302. The selector 302 mayoutput the signals on a pair of sense lines from among the sense linesin all of the measurement lines. For example, FIG. 3 shows that theselector 302 is outputting signals on sense lines M₁₋₄ (see FIG. 2),which are connected to battery cell 14 in battery group 1. The selector302 can therefore provide access to the voltage across any battery cellin the battery pack 1.

The control unit 2 may include a measurement circuit 304 to measure thesignals provided by the selector 302; e.g., the battery voltage across agiven battery cell, current flow through a given battery cell, etc. Themeasurement circuit 304 may provide the voltage level (e.g., as adigital signal) to control logic 306. In general, the measurementcircuit 304 and sense lines can be configure to make measurements onbattery cells (such as shown in the figures), on battery units (see FIG.8A), on battery groups, or on the entire battery pack itself.

The control logic 306 may output control signals (switching signals) onits switching lines S₁-S_(m) to control the ON/OFF state of theswitching elements 12-20. The control logic 306 may operate the selector302 to take measurements of a battery cell (via the measurement circuit304) and operate the switching element connected to that battery cellbased on the measurements; e.g., control the ON times and OFF times ofthe switching element. In accordance with the present disclosure, thecontrol logic 306 can generate control signals based on respectivemeasurements made on the battery cells 3-11 connected to the switchingelements 12-20. In some embodiments, a lookup table 308 can storepreviously measured characteristics of one or more battery cells. Sincethe control signals for each switching element are based on the measuredcharacteristics of the corresponding battery cell, the charging of eachbattery cell in the battery pack can be optimized.

In order to maintain a completed circuit through the battery pack 1 atall times during charging, one or more switching elements in eachbattery group (group 1, group 2, etc.) must be turned ON in order toprovide a path for the charging current to flow from the charger throughat least one battery cell in each battery group. FIG. 4 shows an exampleof a switching state during charging. The figure shows that switch 12 inbattery group 1 is ON (conducting, CLOSED), switch 16 in battery group 2is ON, and so on to switch 19 in battery group M. This switchconfiguration completes a circuit between terminals 21 and 22 of thebattery pack 1 for charging by the charger. Thus, during a chargingprocess in accordance with the present disclosure, the control signalscan control each of the switching elements so that the charging of eachcorresponding battery cell can be optimized, and at the same time,timing of the ON times of switching elements in the battery groups canbe selected so that there is overlap in order to ensure there is alwaysat least one CLOSED switching element in each battery group at all timesduring charging so that a complete circuit between terminals 21 and 22of the battery pack 1 is always present.

In some embodiments, the control unit 2 may “switch in” a single batterycell (i.e., turn ON the switching element corresponding to the batterycell) from each battery group to complete a circuit path betweenterminals 21, 22. This switch configuration is shown in FIG. 4, forexample. In other embodiments, the control unit 2 may use a switchconfiguration that switches in two or more battery cells in a givenbattery group during charging. FIG. 4A, for example, shows a switchconfiguration in which battery cells 3 and 5 in battery group 1 areswitched in, battery cell 7 in battery group 2 is switched in, and so onto battery group M where battery cells 9 and 11 are switched in. Thecontrol unit 2 may turn ON all the switching elements in the batterypack.

FIG. 5 depicts an example of charging voltage waveforms for batterycells of battery pack 1 during pulse charging. The figure shows thetiming in accordance with some embodiments to achieve different switchconfigurations in the battery pack 1 during charging. For purposes ofexplanation, the switch configuration shown in FIG. 4 will be used. Attime c1, the control unit 2 (via its control logic) may turn ONswitching element 13 (via the corresponding control line in the set ofswitching lines S₁) to provide charging current through battery cell 3in battery group 1. Likewise, switching element 16 and so on throughswitching element 19 may be turned ON to provide charging currentthrough respective battery cell 7 and so on to battery cell 10 inrespective battery group 2 and so on to battery group M. Pulse 1 mayrepresent the switching pulse that turns ON switching elements 13, 16and so on to switching element 19 that comprise the first switchconfiguration.

At time c2, the switch configuration may be changed. The switchingelements in the current switch configuration that are turned ON at timec1 will be turned OFF, and the switching elements for the next switchconfiguration will be turned ON. Pulse 2 may represent the switchingpulse that turns ON the switching elements for the next switchconfiguration.

As the timing chart in FIG. 5 indicates, the switching elements for thecurrent switch configuration may be turned OFF at the same time theswitching elements for the next switch configuration are turned ON. Inother words, the falling edge of pulse 1 may coincide in time with therising edge of pulse 2.

Although not shown, in other embodiments, there may be some overlapbetween when the switching elements for the current switch configurationare turned OFF and when the switching elements for the next switchconfiguration are turned ON. In other words, the rising edge of pulse 2may occur earlier in time than the falling edge of pulse 1. This overlapin the timing between switch configurations ensures that chargingcurrent from the charger 4 is always flowing through the battery pack 1;i.e., at least some battery cells are receiving the charging currentfrom the charger 4.

The particular configuration of switching elements depends onconsiderations such as the current carrying capacity of the charger 4.Some chargers have limited current handling, so switch configurationswhere only one battery cell per battery group is switched in may beappropriate. More robust chargers (e.g., chargers that are capable ofhandling high peak pulsed currents) may be able to handle higher currentloads, and so may be able to support switch configurations where two ormore battery cells per battery group are switched in.

In some embodiments, the number of battery cells in a battery group thatare switched in may vary from one charge pulse to another.Considerations for the particular switch configuration include the stateof the charging process (e.g., constant current mode vs. constantvoltage mode, etc.), state of charge of the battery cells, different agepoints of the battery pack 1, and so on.

In some embodiments, sub-groups of battery cells in a battery group maybe switched in parallel without overlap. In some embodiments, where thecharger 4 is a switching power supply, the turning ON and OFF of theswitching elements may be synchronized with switching timing of theswitching power supply.

FIG. 6 shows an embodiment of a battery pack 1′ in accordance with thepresent disclosure. In some embodiments, the battery pack 1′ maycomprise separate control units 2 ₁, 2 ₂, . . . 2 _(m) for therespective battery groups 1, 2, . . . M. The control units 2 ₁, 2 ₂, . .. 2 _(m) may be interconnected in order to coordinate turning ON and OFFthe switching elements; e.g., in order to ensure that each battery grouphas at least one switching element in the CLOSED state in order to closethe circuit between terminals 21 and 22. In other embodiments, some ofthe control units 2 ₁, 2 ₂, . . . 2 _(m) may be configured to controlmultiple battery groups, rather than having the one control unit-to-onebattery group configuration shown in FIG. 6.

FIG. 6A shows an embodiment of a battery pack 1″ in accordance with thepresent disclosure. In some embodiments, the battery pack 1″ maycomprise bypass units between battery groups. The bypass units may beactivated to bypass one or more battery groups. FIG. 6A shows somedetails for a bypass unit 602 in accordance with some embodiments. Thebypass units may be useful for reacting to failure in one or morebattery groups, providing balancing, providing overvoltage protecting onFETs, mitigating transitions of battery cell switching (e.g., compensatefor back EMF), and the like.

FIG. 7 shows an embodiment of a battery group in a battery pack inaccordance with the present disclosure. In some embodiments, the batterycells in a battery group of a battery pack may be switched together.FIG. 7, for example, shows a battery group of battery cells having asub-group of battery cells 71 that are all switched by switching element74 and another sub-group of battery cells 72 that are all switched byswitching element 75. The battery cells in a sub-group (e.g., 71) may bethe same kind of battery cell, or may be different kinds of batterycells (e.g., different capacity, size, shape, etc.). Such variationsinside of the same battery cell subgroup allows for a battery pack thatcan fit in irregularly shaped enclosures. The battery group may containsub-groups of battery cells or a mixture of individual battery cells andsub-groups of battery cells. The battery group in FIG. 7, for example,includes a single battery cell 73 that is switched by its owncorresponding switching element 76.

In some embodiments, one or more battery groups may include alternativestorage elements (e.g., super caps) that can be switched in duringcertain times (e.g., peak load conditions) and then disabled until morefavorable conditions for re-charging exist. In some embodiments, thealternative storage elements may be used as by-pass elements to mitigateswitching between cells during charging to sustain an average currentflow.

In some embodiments, the battery cells in a battery group may bedifferent in capacity, size, shape, charge/discharge rate. Suchvariations inside of the same battery cell subgroup allows for a batterypack that can fit in irregularly shaped enclosures. The use of differentbattery cells in a battery group can accommodate different charge ratesduring partial battery pack charge. Referring to FIG. 8, for example,suppose battery cells 81, 82 are a 3.7 V battery cells with very highrate of charge and battery cells 83 through 84 are regular charge rate3.7 V cells. If a partial ultra fast charge of the battery pack isrequired, then battery cells 81, 82 may be switched in via respectiveswitching elements 85, 86 to partially charge the battery pack using theultra high charging rate of battery cells 81, 82. When a sufficientpartial charge of the battery pack is achieved, the other slowercharging battery cells (e.g., 83-84) may be switched in via respectiveswitching elements 87-88.

FIG. 8A shows that in some embodiments, the battery cells in a batterygroup can be organized in battery units 802. A battery unit can compriseone battery cell (e.g., battery unit 802 a) or two or more battery cellsconnected in series. FIG. 8A, for example shows three battery units,each having two series-connected battery cells 81/81 a, 82/82 a, 83/83a. In other embodiments (not shown) a battery unit can comprise morethan two series-connected battery cells. A battery group can comprisesbattery units having different numbers of battery cells. FIG. 8A, forexample, shows that battery unit 802 comprises two battery cells 83/83a, while battery unit 802 a has a single battery cell 84.

Recall that the controller 2, in accordance with the present disclosure,can use measurements of the battery cells taken during the time ofcharging the battery pack 1 to determine the ON times and OFF times ofthe switching elements to provide optimized charging on a battery cellby battery cell basis; for example by controlling the ON times and OFFtimes (which can be expressed as duty cycles) of switching pulses thatcomprise the control signals to the switching elements.

FIG. 9, for example, shows the parameters of a switching pulse 502 forcharging a battery cell. It will be appreciated that the followingdescription applies to each battery cell in the battery pack 1. Assumefor discussion purposes that the pulse period for switching pulse 502 isT_(period). In some embodiments, the pulse period can be the same foreach pulse. In other embodiments, the pulse period can vary from onepulse to the next; see, for example, commonly owned U.S. applicationSer. No. 15/644,498 filed Jul. 7, 2017, the content of which isincorporated herein by reference in its entirety for all purposes. Theswitching pulse 502 has an ON time (T_(ON)) and an OFF time (T_(OFF)).The duration of T_(ON) and T_(OFF),can be dynamically determined basedon battery measurements 504 made during the ON time of the switchingpulse 502.

The battery measurements 504 can comprise measurements of current flowthrough the battery cell. Current flow through the battery cell cangradually increase from the time t_(ON) that the switching pulse 502 isapplied and follow the flow profile such as shown in FIG. 9. The flowprofile of current through the battery cell depends on factors such asbattery chemistry, state of charge, temperature, and the like. In alithium ion battery, for example, the lithium ions flow from thepositive electrode to the negative electrode through the electrolyte.The electrons and lithium ions combine at the negative electrode anddeposit there. During a charging pulse, charge current saturation canoccur where additional charge current into the battery cell for thatswitching pulse 502 may not be effective and may even be detrimental(e.g., cause heat build up, create mechanical stress).

In accordance with the present disclosure, the controller 2 (e.g.,control logic 306) can analyze or otherwise track the current flow todetect the onset charge current saturation by looking for a change inthe flow profile. Suppose at time t_(DETECT) the controller 2 detectssuch a change in the flow profile. The time of detection t_(DETECT) canbe used to determine the duration T_(ON) of the ON time of the switchingpulse 502, for example, in order to limit the charge current into thebattery cell. A first time period T_(1C) between t_(ON) and t_(DETECT)can be computed by backing off a margin of time Δt₁ from t_(DETECT), forexample, by computing t1=t_(DETECT)−Δt₁. A buffer period 506 comprisingthe margin of time Δt₁ and Δt₂ can be provided around the detection timet_(DETECT) to account for uncertainty in the detection of the onset ofcharge saturation. The first period T_(1C) can be the period betweentime t_(ON) and time t₁.

A second time period T_(2C) can be computed based on keeping the secondtime period within a predetermined range. During the second time periodT_(2C), charge saturation can be a dominant factor during the chargingpulse. In some embodiments, the second time period T_(2C) can bedetermined in order to maintain a certain ratio R between T_(1C) andT_(2C). For example, T_(2C) can be computed from the relation:R=T_(1C)/T_(2C), where R can be a predetermined ratio. The ON timeT_(ON) can be computed as T_(ON)=(T_(1C)+T_(2C)+T_(3C)), where Tac isthe width of the buffer 502. By dynamically computing the ON time foreach switching pulse 502, battery charging can be more efficient,battery damage that inherently arises during charging (e.g., heat buildup) can be reduced (which can contribute to safety), and battery lifecan be extended.

In accordance with the present disclosure, the OFF time T_(OFF) (T_(4C))of the switching pulse 502 can be computed by subtracting the T_(ON)from the selected pulse period T_(period). However, if the resulting OFFtime is too long, then overall battery charging time can be increased,which is typically undesirable. Accordingly, in accordance with thepresent disclosure if the T_(OFF), exceeds a predetermined maximum timeMaxOffTime, T_(OFF) can be set to MaxOffTime.

If, on the other hand, the resulting OFF time is too short, then theremay not be enough recovery time for various chemical reactions in thebattery cell to run their course before the onset of the next chargingpulse; more time may be needed. Accordingly, in accordance with thepresent disclosure, if the T_(OFF) becomes less than a predeterminedminimum time MinOffTime, T_(OFF) can be set to MinOffTime to allow timefor the chemical reactions to take place before initiating the nextcharging pulse. As a consequence, the actual pulse period of theswitching pulse 502 will be different from the selected pulse periodT_(period).

As noted above, in accordance with the present disclosure, the switchingelements 12-20 of the battery pack 1 may be controlled such that thecharge current from the charger 4 flowing into the battery pack 1through terminals 21 and 22 is uninterrupted at all times while thebattery pack is being charged. In some embodiments, for example, theswitching pulses provided to the battery groups (group 1, group 2, etc.)can be adjusted (e.g., by lengthening or shortening OFF times, T_(OFF))so that the ON times of at least one switching pulse in each batterygroup overlap with one another so that a complete circuit can be createdthrough each battery group (e.g., FIG. 4).

The amplitude of the charging current of the charging pulse can varyfrom one charging pulse to the next, during the charging process. Theinventors of the present disclosure have noted that the OFF time of onecharging pulse can affect the charging current amplitude. Accordingly,in some embodiments, rather than basing the OFF time on the selectedpulse period T_(period), the OFF time can be varied between MinOffTimeand MaxOffTime in response to the amplitude of the charging current I.

In some embodiments, the output voltage of the charger 4 can be selectedfor different switching pulses 502. A reason for doing this might be tolimit the “headroom” for the current of the switching pulse 502. Thebattery impedance can be a highly dynamic parameter whose value canchange very quickly. It can be impractical, and in some cases may not befeasible, to use a conventional feedback loop to control the chargingcurrent to accommodate for a changing battery impedance. In accordancewith some aspects of the present disclosure, the output voltage of thecharger 4 can be adjusted to limit its output level so that the currentflow into the battery cell does not exceed safety levels. For example,suppose the safety limit sets a peak charging current of the batterycell to be 35 A. If we expect the battery cell to have a minimum batteryimpedance of 100 mΩ and an open circuit voltage (OCV) of 3.5 V, thisestablishes a 11V output voltage for the charger 4:

3.5V+35 A×0.1Ω=11V.

In other embodiments, instead of limiting the output voltage of thecharger 4, the switching element connected to the battery cell can beused to limit the flow of charging current into battery cell. In thecase of an FET type switching element, for example, the controller 2 canproduce an analog output to adjust the gate-source voltage of the FETand hence the device channel saturation of the FET, to control thecharging current into the battery cell.

The battery impedance can change dynamically from one charging pulse toanother. For a given charging pulse, the battery impedance can be atsome initial value at the beginning of the charging pulse and at somehigher value at the end of the charging pulse. The impedance changeduring the pulse period can be non-linear in time. The lowest andhighest values of the battery impedance during a given charging pulsecan vary during the charging process. These impedance changes can bepredicted based on impedance values previously recorded during othercharges of the battery or based on a mathematical model of the battery.

FIG. 10 illustrates an example of detecting a change in the current flowthrough the battery cell that can be indicative of the onset of chargecurrent saturation. In some embodiments, for example, the flow profilemay include a exponential decay portion and a linear decay portion. Theslope of the flow profile can be monitored to detect the transitionbetween the exponential decay portion and the linear decay portion. Forexample, the slope can be monitored at the onset of the charging pulseat time t_(ON). In some embodiments, the monitoring can begin at sometime after t_(ON), since saturation does not happen right away. In someembodiments, the rate of change of the slope (i.e., second derivative ofthe flow profile) can be used to determine when the change in thecurrent flow through the battery has occurred. In other embodiments, wecan monitor for the rate of change of the rate of change (i.e., a thirdderivative) of the charging current. In particular, we can detect for achange in the sign of the third derivative.

It will be appreciated that other detection techniques can be used. Insome embodiments, for example, the change can be associated withswitching from exponential current decline into linear current decline.In other embodiments, detection can be based on switching from oneexponential decline into another much slower exponential decline, and soon.

Referring to FIG. 11, the discussion will now turn to a high leveldescription of processing in the controller 2 for generating controlsignals to operate switching elements 12-20 when charging the batterypack 1 in accordance with the present disclosure. In some embodiments,for example, the controller 2 may include computer executable programcode or equivalent firmware (e.g., field programmable gate array, FPGA),which when executed cause the controller 2 to perform the processing inaccordance with FIG. 11. The flow of operations performed by thecontroller 2 is not necessarily limited to the order of operationsshown.

At block 1102, the controller 2 can produce a control signal for eachswitching element 11-20 in the battery pack 1 according to the followingduring charging of the battery pack. The control signal comprises aplurality of control pulses, that control the ON/OFF state of thecorresponding switching element to provide pulse charging of batterycell(s) comprising the battery unit (e.g., 802 a, FIG. 8A) connected tothe switching element.

At block 1104, the controller 2 can select a pulse period for the givencontrol pulse. In some embodiments, the pulse period can be the same foreach switching element. In other embodiments, the pulse period can varydepending on the switching element. In other embodiments, the pulseperiod can very from one period to another, and so on.

At block 1106, the controller 2 can output the control pulse to turn ONthe switching element, thus providing a charging pulse to the batterycell(s) for the duration of the ON time of the charging pulse.

At block 1108, the controller 2 can sense current flow through thebattery unit connected to the switching element, in some embodiments.

At block 1110, the controller 2 can analyze the battery measurements todetect a change in current flow through the battery cell, which forexample, may indicate the onset of charge current saturation in thebattery cell. If a change in the flow profile has not been detected(e.g., per FIG. 10), the controller 2 can return to block 1108.Otherwise, processing can continue to block 1112.

At block 1112, the controller 2 can determine the duration of the ONtime T_(ON) of the charging pulse such as explained, for example, inconnection with FIG. 10, for example.

At block 1114, the controller 2 can determine the OFF time T_(OFF), ofthe charging pulse. If the ON time for the charging pulse is short, thatcan result in too long of an OFF time; in which case, T_(OFF) can be setto MaxOffTime. Conversely, if the ON time for the charging pulse islong, that can result in too short of an OFF time; in which case,T_(OFF), can be set to MinOffTime. As noted above, in accordance withthe present disclosure, the switching elements 12-20 of the battery pack1 may be controlled such that the charge current from the charger 4flowing into the battery pack 1 through terminals 21 and 22 isuninterrupted at all times while the battery pack is being charged. Insome embodiments, for example, the controller 2 can coordinate thepulses provided to the battery groups (e.g., by increasing or decreasingthe OFF times, T_(OFF)) so that the ON times of at least one pulse ineach battery group overlap with one another in order to create acomplete circuit through each battery group between terminals 21 and 22(e.g., FIG. 4).

At block 1116, the controller 2 can turn OFF the switching element atthe end of the ON time determined at block 1112 to interrupt the flow ofcharging current from the charger 4 through the battery unit connectedto the switching element.

At block 1118, the controller 2 can delay for a period of time equal toT_(OFF), before initiating the next charging pulse. During this delayperiod, the interruption of charging current from the charger 4 throughthe battery unit can be a complete interruption if the switching elementis fully OFF (i.e., no flow of charging current to the battery). In someembodiments, during this delay period, some flow of current from thecharger 4 can be provided through the battery unit, for example, bypartially turning OFF the switching element or controlling the charger 4to provide a small amount of trickle current through the battery unit.In other embodiments, the charger 4 can be controlled to create areverse flow of current through the battery unit; e.g., a dischargecurrent.

The above flow was described using measurements of current flow throughthe battery unit as the criterion for controlling the switching element.In other embodiments, the measurement circuit (e.g., 304) can beconfigured to measure characteristics in addition to or instead ofcurrent flow (e.g., battery voltage), which the controller 2 can use asa basis for controlling the switching element.

The above description illustrates various embodiments of the presentdisclosure along with examples of how aspects of the particularembodiments may be implemented. The above examples should not be deemedto be the only embodiments, and are presented to illustrate theflexibility and advantages of the particular embodiments as defined bythe following claims. Based on the above disclosure and the followingclaims, other arrangements, embodiments, implementations and equivalentsmay be employed without departing from the scope of the presentdisclosure as defined by the claims.

What is claimed is:
 1. A system, comprising: one or more battery units,wherein each battery unit comprises one or more battery cells; one ormore switches that are operatively coupled to one or more battery units;and a controller configured to: generate a plurality of pulsed switchsignals to control the one or more switches, wherein: each battery unitgets pulse charged, via a corresponding switch, based on a correspondingswitch signal, each pulsed switch signal corresponds to at least one ofthe one or more switches, each pulsed switch signal comprises a seriesof pulses, each pulse having an ON time and an OFF time, which aredynamically determined based on one or more characteristics of a batteryunit associated with the corresponding switch, and the one or morecharacteristics are measured during the ON time of the pulse.
 2. Thesystem of claim 1, wherein the controller is further configured tomeasure one or more characteristics of the one or more battery units andthe one or more battery cells.
 3. The system of claim 1, wherein the oneor more battery units comprise a plurality of series-connected batterygroups, and wherein each battery group, of the plurality ofseries-connected battery groups, comprises a plurality ofparallel-connected switched battery units.
 4. The system of claim 3,wherein each switched battery unit, of the plurality ofparallel-connected switched battery units, comprises one or moreseries-connected battery cells connected to a corresponding switch ofthe one or more switches.
 5. The system of claim 1, further comprising:one or more measurement circuits operatively coupled to the one or morebattery units and the controller; and one or more pulse generatorsoperatively coupled to the one or more battery units and the controller.6. The system of claim 1, further comprising a lookup table that isconfigured to store previously measured characteristics of the one ormore battery units, wherein at least some of the one or morecharacteristics are accessed from the lookup table.
 7. The system ofclaim 1, wherein the controller is configured to control an ON/OFF stateof the one or more switches to provide a path for an uninterrupted flowof charging current through the one or more battery units.
 8. The systemof claim 1, wherein the one or more characteristics measured during theON time of the pulse includes at least a respective rate of change ofcharging current through the one or more battery units.
 9. A method tocharge a battery pack comprising one or more battery units and one ormore switches, wherein each battery unit comprises one or more batterycells, and one or more switches are operatively coupled to the one ormore battery units, the method comprising: generate a plurality ofpulsed switch signals to control the one or more switches, wherein: eachbattery unit gets pulse charged, via a corresponding switch, based on acorresponding switch signal, each pulsed switch signal corresponds to atleast one of the one or more switches, each pulsed switch signalcomprises a series of pulses, each pulse having an ON time and an OFFtime, which are dynamically determined based on one or morecharacteristics of a battery unit associated with the correspondingswitch, and the one or more characteristics are measured during the ONtime of the pulse.
 10. The method of claim 9, wherein the one or morebattery units comprise a plurality of series-connected battery groups,wherein each battery group, of the plurality of series-connected batterygroups, comprises a plurality of parallel-connected switched batteryunits, and wherein each switched battery unit, of the plurality ofparallel-connected switched battery units, comprises one or moreseries-connected battery cells connected to a corresponding switch ofthe one or more switches.
 11. The method of claim 9, further comprisingaccessing a lookup table, which stores previously measuredcharacteristics of the one or more battery cells, to obtain at leastsome characteristics of the one or more battery cells.
 12. The method ofclaim 9, further comprising providing a path for an uninterrupted flowof charging current through the one or more battery units.
 13. Themethod of claim 12, wherein providing the path for the uninterruptedflow of charging current includes overlapping the ON time of one or morepulses of the pulsed switch signals for each battery unit.
 14. Themethod of claim 9, wherein the one or more characteristics measuredduring the ON time of the pulse includes at least a respective rate ofchange of charging current through the one or more battery units.
 15. Acontroller to control a battery pack comprising one or more batteryunits and one or more switches, wherein each battery unit comprises oneor more battery cells, wherein one or more switches are operativelycoupled to the one or more battery units, and wherein the controller isconfigured to: generate a plurality of pulsed switch signals to controlthe one or more switches, wherein: each battery unit gets pulse charged,via a corresponding switch, based on a corresponding switch signal, eachpulsed switch signal corresponds to at least one of the one or moreswitches, each pulsed switch signal comprises a series of pulses, eachpulse having ON time and OFF time, which are dynamically determinedbased on one or more characteristics of a battery unit associated withthe corresponding switch, and the one or more characteristics aremeasured during the ON time of the pulse.
 16. The controller of claim15, wherein the controller comprises a first circuitry to make one ormore measurements for the one or more battery units, and a secondcircuitry to generate the plurality of pulsed switch signals.
 17. Thecontroller of claim 15, wherein the controller is further configured toaccess a lookup table that stores previously measured characteristics ofthe one or more battery units, and wherein at least some of the one ormore characteristics are accessible from the lookup table.
 18. Thecontroller of claim 15, wherein the controller is configured to controlan ON/OFF state of the one or more switches to provide a path for anuninterrupted flow of charging current through the one or more batteryunits.
 19. The controller of claim 15, wherein the one or morecharacteristics measured during the ON time of the pulse includes atleast a respective rate of change of charging current through the one ormore battery units.
 20. The controller of claim 15, wherein thecontroller comprises: a plurality of measurement circuits, wherein eachmeasurement circuit is associated with at least one of the one or morebattery units, or with at least one of the one or more battery cells,and a plurality of pulse generators, wherein each pulse generator isassociated with at least one of the one or more battery units.